The development of a cell in higher organisms is characterized by the fixing and subsequent maintenance of its commitment to differentiate as a particular cell type. Organizing alternative commitments by cells sitting side by side results in the growth of specialized tissues and structures. The Drosophila homeotic gene Antennapedia plays a role in decisions about developmental pathways and therefore presents a system to study these processes. We know that different mutations of Antennapedia can result in different phenotypes, such as head cells that normally form an antenna instead developing as second leg or the eye developing as wing. We have cloned the Antennapedia locus and isolated three structurally different Antennapedia cDNAs which we believe could represent RNAs encoding three different Antennapedia functions. The DNA sequence of one is completed and the sequences of the other two will be finished in several months. To address the question of how the Antennapedia gene product acts to control differentiation pathways, three approaches are proposed. (1) Localize the different RNAs in tissue sections by in situ hybridization to determine which cells make each RNA and how this synthesis pattern is altered in Antennapedia mutant animals. (2) Generate antibodies against the Antennapedia peptide to localize within cells where the gene product resides. (3) Inject embryos with anti-sense single stranded nucleic acid so as to deplete specific Antennapedia mRNAs and thereby assign phenotypes to the loss of particular mRNAs. These experiments are prerequisites for the purification and direct biochemical assay for function of the Antennapedia gene product which is our long term goal.